The present invention relates generally to gas turbine engines, and, more specifically, to the film cooling of turbine rotor blades and vanes.
A gas turbine engine includes a compressor for compressing air which is channeled to a combustor wherein it is mixed with fuel and ignited for generating combustion gases. The combustion gases flow downstream through one or more turbines which extract energy therefrom for powering the compressor and producing output power. Turbine rotor blades and stationary nozzle vanes found in the high pressure turbine disposed immediately downstream from the combustor are typically supplied with a portion of compressed air bled from the compressor for cooling these components to effect a useful life thereof. Both the rotor blades and stator vanes have airfoils including pressure and suction sides over which the combustion gases flow during operation. The airfoils typically include serpentine cooling passages therein in which the cooling bleed air is channeled and discharged from the airfoils through film cooling holes spread over the outer surfaces thereof.
In film cooling, the cooling air must be channeled through the airfoils with a suitably high pressure to prevent backflow ingestion of the hot combustion gases through the film cooling holes, while at the same time avoiding excessive pressure drop across the film cooling holes which would tend to separate the film from the outer surface of the airfoils which would substantially degrade film cooling effectiveness. Film cooling art is crowded with various film cooling hole designs which attempt to effect the best film cooling possible with minimum film separation tendency and a suitable backflow margin to prevent ingestion of the hot combustion gases. The substantial number of prior art film cooling designs clearly evidence the difficulty in achieving this compromise, with minor variations in film cooling geometry providing significant performance changes in an ongoing attempt to maximize cooling efficiency while reducing the use of parasitic bleed air.